"use client";

import { useCallback, useEffect, useMemo, useState } from "react";

export interface PinnedPair {
  fromCode: string;
  toCode: string;
}

const PINNED_PAIRS_STORAGE_KEY = "nexcurrency:pinned-pairs:v1";
const CODE_PATTERN = /^[A-Z0-9]{2,12}$/;

function normalizeCode(value: unknown): string | null {
  if (typeof value !== "string") {
    return null;
  }

  const normalized = value.trim().toUpperCase();

  if (!CODE_PATTERN.test(normalized)) {
    return null;
  }

  return normalized;
}

function normalizePair(value: unknown): PinnedPair | null {
  if (!value || typeof value !== "object") {
    return null;
  }

  const record = value as Record<string, unknown>;
  const fromCode = normalizeCode(record.fromCode);
  const toCode = normalizeCode(record.toCode);

  if (!fromCode || !toCode || fromCode === toCode) {
    return null;
  }

  return { fromCode, toCode };
}

function toPairKey(pair: PinnedPair): string {
  return `${pair.fromCode}:${pair.toCode}`;
}

function dedupeAndClampPairs(pairs: PinnedPair[], limit: number): PinnedPair[] {
  const keys = new Set<string>();
  const normalized: PinnedPair[] = [];

  for (const pair of pairs) {
    const key = toPairKey(pair);

    if (keys.has(key)) {
      continue;
    }

    keys.add(key);
    normalized.push(pair);

    if (normalized.length >= limit) {
      break;
    }
  }

  return normalized;
}

export function usePinnedPairs(limit = 6) {
  const [pinnedPairs, setPinnedPairs] = useState<PinnedPair[]>([]);
  const [isReady, setIsReady] = useState(false);
  const isLimitReached = pinnedPairs.length >= limit;

  useEffect(() => {
    if (typeof window === "undefined") {
      return;
    }

    try {
      const raw = window.localStorage.getItem(PINNED_PAIRS_STORAGE_KEY);

      if (!raw) {
        setPinnedPairs([]);
        setIsReady(true);
        return;
      }

      const parsed = JSON.parse(raw) as unknown;
      const parsedPairs = Array.isArray(parsed)
        ? parsed.map(normalizePair).filter((pair): pair is PinnedPair => pair !== null)
        : [];

      setPinnedPairs(dedupeAndClampPairs(parsedPairs, limit));
    } catch {
      setPinnedPairs([]);
    } finally {
      setIsReady(true);
    }
  }, [limit]);

  useEffect(() => {
    if (!isReady || typeof window === "undefined") {
      return;
    }

    try {
      window.localStorage.setItem(
        PINNED_PAIRS_STORAGE_KEY,
        JSON.stringify(pinnedPairs),
      );
    } catch {
      // Intentionally ignored: localStorage may be unavailable.
    }
  }, [isReady, pinnedPairs]);

  const isPinnedPair = useCallback(
    (pair: PinnedPair) => pinnedPairs.some((entry) => toPairKey(entry) === toPairKey(pair)),
    [pinnedPairs],
  );

  const addPinnedPair = useCallback(
    (pair: PinnedPair) => {
      const normalized = normalizePair(pair);

      if (!normalized) {
        return;
      }

      setPinnedPairs((current) => {
        const exists = current.some(
          (entry) => toPairKey(entry) === toPairKey(normalized),
        );

        if (!exists && current.length >= limit) {
          return current;
        }

        return dedupeAndClampPairs(
          [
            normalized,
            ...current.filter((entry) => toPairKey(entry) !== toPairKey(normalized)),
          ],
          limit,
        );
      });
    },
    [limit],
  );

  const removePinnedPair = useCallback((pair: PinnedPair) => {
    const normalized = normalizePair(pair);

    if (!normalized) {
      return;
    }

    setPinnedPairs((current) =>
      current.filter((entry) => toPairKey(entry) !== toPairKey(normalized)),
    );
  }, []);

  const togglePinnedPair = useCallback(
    (pair: PinnedPair) => {
      if (isPinnedPair(pair)) {
        removePinnedPair(pair);
        return;
      }

      addPinnedPair(pair);
    },
    [addPinnedPair, isPinnedPair, removePinnedPair],
  );

  return useMemo(
    () => ({
      pinnedPairs,
      isReady,
      isLimitReached,
      isPinnedPair,
      addPinnedPair,
      removePinnedPair,
      togglePinnedPair,
      limit,
    }),
    [
      pinnedPairs,
      isReady,
      isLimitReached,
      isPinnedPair,
      addPinnedPair,
      removePinnedPair,
      togglePinnedPair,
      limit,
    ],
  );
}